Static eliminator



NOV. 2, 1943. a SLAYTER 2,333,213

STATIC ELIMINATOR Filed Feb. 2, 1942 III IIIIIII IIIIIIIII I INVENTOR.

GAMES SLAYTER 52 BY ATTORNEY Patented Nov. 2, 1943 UNITED STATES PATENTOFFICE STATIC ELIMINATOR Games Slayter, Newark, Ohio ApplicationFebruary 2,1942, Serial No. 429,216 8 Claims. (01'. 175-264) Thisinvention relates generally to electric discharge apparatus and refersmore particularly to improvements in equipment of the type employed toeliminate the interference caused by static electricity.

It has been proposed to eliminate interference resulting from staticconditions by providing an electric discharge of alternating polaritybetween an emitting electrode and a collecting electrode so arranged inan alternating current circuit with respect to the electrically chargedobject that ions drift from the electrostatic field between theelectrodes to neutralize'the charge on the object.

Although electric discharge equipment operating on the principle brieflyoutlined above has proved successful under widely varying conditions,nevertheless, the rate at which one electric discharge device is capableof operating to effect neutralization is not always sufficient toneutralize a relatively fast moving heavily charged material. Thislimitation is overcome to some extent by providing a series of electricdischarge devices but this procedure complicates the installation andincreases the cost of the equipment as well as the expense of operation.

It is, therefore, one of the principal objects of this invention to.overcome the above limitation without appreciably increasing the costof the equipment or the expense of operating the latter by providing anelectric discharge device having means for neutralizing a large quantityof charge of either polarity on a fast moving object before the object,registers with the electrostatic field produced by the emitting andcollecting electrodes.

More particularly the present invention contemplates supporting one ormore grounded pointed rods or electrodes in such relationship to thecharged body that when the potential difference between the body andground exceeds the onset? potential of the pointed electrodes, anelectric discharge is created from the pointed ends of the electrodesand this discharge reduces the potential of the object to'the onsetpotential of the pointed electrodes. The onset potential of the pointedrods is usually small as compared to the total charge on the object andthe electrical charge on the object represented by this onset potentialis readily neutralized by the electric discharge device when the objecthas advanced. to a position in registration therewith.

made more apparent as this description proceeds,

and especially rapidly moving objects.

especially when considered in connection with the accompanying drawingwherein:

Figure 1 is a side elevational view partly in section of electricdischarge equipment constructed in accordance with this invention;

Figure 2 is a cross sectional view taken on the line 2-2 of Figure 1 andshowing the equipment in operative relation to a charged object; and

Figure 3 is a diagrammatic perspective view of the electric dischargeequipment-and showing a part of the electrical circuit employed.

Although the electric discharge equipment forming the subject matter ofthis invention may be advantageously used in practically any case whereit is desired to release or neutralize electrostatic charges,nevertheless, it finds particular utility when used for the purpose ofremoving or neutralizing static charges on moving objects For thepurpose of illustrating this invention, therefore, I havediagrammatically shown in Figure 2 a travelling object l0 which may be asheet of paper or any other materialadapted to acquire an electriccharge of either polarity.

It is desired to neutralize static charges on travelling sheets ofmaterial because these charges often times seriously interferewith-processing the material and this invention insures expedientneutralization of charges of either polarity on the sheet of material IDas the latter is advanced along its path of travel. In general, theequipment for accomplishing the above results comprises an electricdischarge device ll having a plurality of pointed emitting electrodes l2arranged in spaced relation to each other ina single row and havingcollecting electrodes l3, respectively, supported at opposite sides ofthe emitting electrodes in lateral spaced relation to the latter. I

As shown in Figure 3, the electrodes are connected in an electriccircuit 14 which includes an alternating current transformer l5 having aprimary winding l6 connected to a source of alternating current andhaving a secondary winding l6. One end of the secondary winding I 8' isgrounded as at I! and the other end of the secondary winding iselectrically connected to each of the emitting electrodes I2. Thecollecting electrodes l3 are arranged in the circuit It in such a mannerthat they are also connected to the ground l1. As a result of the abovecircuit arrangement, a difference of alternating potential is connectedto the emitting electrodes l2 and the collecting electrodes I3.

The difference of potential is predetermined in dependence upon thespacing between the emitting electrodes i2 and the collecting electrodesl3 so that an electric discharge of alternating polarity takes placebetween the pointed ends of the emitting electrodes l2 and thecollecting electrodes. In other words, the arrangement is such thatelectrostatic fields of opposite polarity are produced between theelectrodes on successive half cycles of operation so that both positiveand negative charges are available in the gap between the electrodes. Ifdesired, a suitable condenser l8 may be connected in the circuit toequalize the quantities of both positive and negative charges producedin the gap between the electrodes on successive half cycles ofoperation.

The electric discharge device I l is shown in Figure 2 as positioned inrelatively close proximity to the underside of the sheet of material Illso as to-influenceany electric charge on this sheet of material. Therelationship between the electrostatic field produced by the device IIand the sheet of material in is such that when the latter is chargedwith a negative polarity, positive charges drift from the electrostaticfield to the sheet of material 10 during the positive half cycle ofoperation of the device ll. Thus, during each positive halt cycle ofoperation of the electric discharge device ll, positive charges aresupplied to the negatively charged sheet of material l0 and the lattereventually becomes neutralized. On the other hand, if the sheet ofmaterial Ill carries a positive charge, negative charges are releasedfrom the electrostatic field during the negative half cycle of operationof the device II and are supplied to the sheet of material "I toneutralize the latter. It follows, therefore, that the electricdischarge device ll acts to neutralize the sheet of material Illregardless of the polarity of the charge on the latter.

In some instances the quantity of electrical charge on the sheet ofmaterial II and the rate of travel of this sheet is such that theelectric discharge device ll does not operate with suflicient rapidityto completely neutralize the electric charge on the sheet of materialIII. In order to overcome this objection, the action of the electricdischarge device I I is supplemented byone or more rows of pointeddischarge electrodes l9. Although the number of rows of dischargeelectrodes I! are not critical and may be varied to suit diiferentconditions, nevertheless, I have shown two distinct rows of dischargeelectrodes I! herein for the purpose of illustration.

In general, the two rows of discharge electrodes I! are spaced laterallyfrom each other a sumcient distance so that the electrodes in one row donot interfere with the electrodes in the other row and the electrodes ineach row are spaced from each other a suflicient distance so that theydo not interfere with one another. In addition, the electrodes in eachrow are electrically connected in series and are also electricallyconnectedtothe ground ll. Inthepresentinstance the discharge electrodesI! are carried by the right hand collecting electrode l3 shown in Figure2 and are pointed toward the underside of the sheet of material II. thistime that both rows of the discharge electrods I! are spaced in advanceof the adjacent collecting electrode I! a suflicient distance that theydo not interfere with the electrostatic field produced between theemitting electrodes I2 and the collecting electrodes l3.

Owing to the above construction, the discharge electrodes I! operate toneutralize a substantial quantity of the electric charge on the sheet 01material It before the latter comes under the It may be pointed out atinfluence of the electrostatic field produced by the electric dischargedevice II. It will, of course, be understood, however, that the pointeddischarge electrodes 18 will not entirely neutralize the charge on thesheet ofmaterlal l0 because these electrodes have a certain resistancewhich is commonly referred to as the onset. potential characteristic.This potential characteristic varies in dependence on the sharpness ofthe emitting tips of the discharge electrodes and, in the presentinstance, the emitting tips are very sharp. As a result, the electrodesl9 are very sensitive and function to initiate the desired electricdischarge upon a relatively small potential difference between the sheetand discharge electrodes. This action is desirable because it renders itpossible to more nearly neutralize the charge on the sheet before thelatter registers -with or comes under the influence of the ionic fieldproduced by the electric discharge device ll.

It follows from the above that if the electric charge on the sheet ofmaterial I0 is suflicient to cause the sheet to have a potential withrespect to ground greater than the onset" potential for electricaldischarge from the pointed electrodes l9, then an electric dischargetakes place at the pointed ends and the potential of the paper withrespect to ground is thereby reduced to the onset" potential of thepointed discharge electrodes IS. The electric charge remaining on thesheet of material I0 is neutralized by the electrostatic field producedby the electric discharge device I I and, as a result, the charge onthe'sheet of material II is completely neutralized.

Assuming, for example, that the electric charge on the sheet of materialIII is of negative polarity, it will be noted that the dischargeelectrodes l9 are of a positive polarity with respect to the sheet l0because they are connected to ground. As a result, an lectric dischargeis produced between the pointed ends of the discharge electrodes l9 andthe sheet II and electrons are drawn from the sheet ll tending to reducethe potential of the sheet to the onset" potential of the pointeddischarge electrodes l9. It may be pointed out that the electronsapproaching the points of the electrodes l9 are accelerated by the moreintense field in the regions of the points and this produces ionization.The positive ions thus produced are forced back toward the sheet ofmaterial ll because the latter is of negative polarity and, accordingly,these positive ions assist in effecting neutralization of the charge onthe sheet of material ll.

Asuming now that the charge on the sheet II is of a positive polarity,it will be noted that the electrodes I! will be of a negative polaritywith respect to the sheet II. This results in an electric discharge fromthe pointed ends of the electrodes is to the sheet II and causeselectrons to accumulate on the sheet ll tending to neutralize thelatter. Thus, it will be apparent that the combination of the electrodesI! and the electric discharge device ll renders it possible tocompletely neutralize the charge on the sheet ll even though this chargeis relafively heavy and even though the rate of travel of the sheet isrelatively fast.

The specific construction of the electric dischargedevice ll selectedherein forthepurpose of illustration is similar to the electrlcdischarge device shown and described in the John Thomay application,Serial No. 413,965, filed October '1,

- ing material and this material is supported on a cylinder 23 ofdielectrical material. The sleeve 22 may be either a semi-conductinginli or a semiconducting paper and in either case possesses sumcient.resistive characteristics to not only assist in controlling theelectricdischarge but also functions as a resistance between adjacent emittingelectrodes I2. As a result, the current drawn by any one emittingelectrode is limited and this is advantageous because it minimizes thetendency for the emitters to become overloaded to the point of arcing.

The electrical conductor 2| projects through one end of the dielectrictube 20 and is electrically connected to the secondary coil l6 of thealternating current transformer I! in the manner shown in the diagram inFigure 3. After the electrical conductor 2| and the cylinder 23, withthe semi-conducting material 22 thereon, are assembled in the tube 20,the opposite ends of the latter are sealed with suitable plugs 24. Theseplugs are formed of a dielectric material and extend beyond the oppositeends of the tube 20 a sufficient distance to enable the device to bereadily mounted The collecting electrodes I3 are supported at oppositeends in end plates 25 which are also formed of dielectric material. Theend plates 25 are apertured to respectively receive the projecting plugs2i and are preferably rigidly secured to the tube 20. This constructionis advantageous because it provides for sealing the electrical conductorand its electrical connection to the emitting electrodes from theatmosphere so that the discharge device will operate satisfactorily inmoisture laden atmospheres without the danger of short circuiting.

It is also important to control the electric. discharge in the gapbetween the emitting electrodes l2 and the collecting electrodes ii inorder to prevent this discharge from becoming disruptive in nature. Inother words, it is desired to provide a diffuse discharge in the gap andthis discharge is one which is free from sparking, arcing andstreamering.

The diffuse discharge is obtained by controlling the maximum currenttendency which can occur in the gap between the emitting electrodes andthe collecting electrodes. This control is dependent on a number ofvariables which vary in dependence upon different uses of the electricdis-.

charge device and to some extent on the power supplied to the circuit H.Therefore, it is not practical to define specific values for thesevariables which will afl'ord the maximum efficiency of operation underall conditions. However, an electric discharge device constructed inaccordance with the following specifications has been found to producethe desired diffuse discharge in the gap between the electrodes. It isto be understood, however, that the specific values noted below aremerely for the purpose of illustrating one particular use of theelectric discharge device and should not be considered as limiting thisinvention.

Assuming for the purpose of this description a 10,000 volt tranformer isused in the circuit and that this transformer has an operating out- .putof approximately 200 microamperes when the primary is connected to a 110volt alternating current source, it has been found that the tips of theemitting electrodes i2 should be approximately three-fourths of an inchfrom the collecting electrodes i3. It has also been found that the tipdiameter of the emitting electrodes should be relatively small andparticular satisfactory results have been obtained by forming the tipsof the emitting electrodes l2 of approximately two thousandths of aninch in diameter. Also adjacent emitting electrodes l2 should be spacedfrom each other a sumcient distance-that thedischarge from the tip ofone emitting electrode does not interfere with the discharge from thetip of adjacent electrodes.

The blocking condenser l8 employed in the circuit M to equalize thedischarges of opposite polarities may be of a relatively small capacity,and I have found that a 2,000 volt condenser having approximately .01microfarad capacity is zrtisfactory under average conditions of opera-The resistivity of the electrical connection 23 between the emittingelectrodes l2 and the electrical conductor 2| is not particularlycritical. However, it is desired to embody some resistance in thecircuit because it has been found that such practice stabilizes theoperation of the device and assists in obtaining a diffuse dischargeover a long period of use with the minimum attention. For the purpose ofillustration a resistance of approximately 200 megohms is satisfactoryto perform the desired results.

The pointed discharge electrodes is are carried by one of the collectingelectrodes l3 and are electrically connected to the latter collectingelectrode in order to have the same potential as this electrode. Asshown in Figure 3, the discharge electrodes in each row are anchored toa conducting rod 26 in such a manner that the discharge electrodes ineach row are electrically connected together in series. The twoconductor rods 26 are connected together at longitudinally spaced pointsby means of a conductor rod 21 and the rod 26 adjacent the collectingelectrode I3 is similarly connected to the electrode l3 by means ofconductor rods 28. Thus, it will be seen that the discharge electrodes[9 form a unit with th; Ielectric discharge device ll.

e spacing between adjacent rows of i electrodes is and the spacingbetweenili e l ei trodes in each row is such that the electrostaticfield at the tip of any one of the electrodes is not disrupted oraffected by the discharge from the tip of adJacent electrodes. Thisspacing will depend to some extent on the distance between the tips ofdischarge electrodes 9 and the travelling sheet of material [0. However,in most applications the distance between adjacent electrodes i9shouldbe within the range of onequarter inch to one-half inch. Also thedistance between the electric discharge electrodes l9 and the device His predetermined so that the discharge electrodes l9 have no effect onthe electrostatic field in the gap between the emitting electrodes l2and the collecting electrodes l3. In

addition, the number of discharge electrodes l9 is determined for eachapplication so that the current is equally divided between a sufiicientnumber of electrodes to avoid overloading any one electrode to the pointwhere the discharge becomes disruptive and produces streamering,

arcing and sparking conditions. This is important because it enables theequirment to be safely used under practically any existing conditions.

What I claim as my invention is:

11. Electric discharge equipment comprising an emitting electrode and acollecting electrode connected in a circuit with-a source of alternatingpotential in a manner to provide an electric discharge oi alternatingpolarity from the emitting electrode to the collecting electrode, and adischarge electrode connected in the circuit and having the samepotential as the collecting electrode. 4

2. Electric discharge equipment comprising a row of pointed emittingelectrodes spaced from each other and serially electrically connectedtogether, a collecting electrode supported on each side of the row ofemitting electrodes in such relation to the pointed ends of the emittingelectrodes to enable a discharge of electriciiw from the pointed ends ofsaid emitting electrodes to the collecting electrodes, and a second rowof pointed discharge electrodes spaced laterally from the row ofemitting electrodes and electrically connected to said collectingelectrodes.

3. Electric discharge equipment comprising an emitting electrode and acollecting electrode connected in a circuit with a source of alternatingpotential and spaced from each other to provide an electric discharge ofalternating polarity in the gap between the electrodes, means in thecircuit providing an electric discharge in the gap of only one polarityat one time, and an additional discharge electrode having the samepotential as the collecting electrode and spaced sufliciently from theemitting electrode to be substantially free from the electrostatic fieldin the gap between the emitting and collecting electrodes.

4. Electric discharge equipment comprising a row of pointed emittingelectrodes spaced from each other and serially electrically connectedtogether, an electric circuit including the emitting electrodes and asource of alternating .potential, a common collecting electrode for saidemitting electrodes and connected in the circuit in such spaced relationto the pointed ends of the emitting electrodes to provide an electricdischarge of alternating po'larityin the gap between said electrodes,and a row of discharge electrodes extending in the same generaldirection as the emitting electrodes and having the same polarity as thecollecting electrode, said discharge electrodes being spaced laterallyfrom the emitting electrodes a sumcientdistance to be substantially freefrom the influence of the electrostatic held in the gap between theemitting and col- .lecting electrodes.

5. 'Eflectric discharge equipment for neutraliza charge of electricityon a travelling object, comprising a discharge electrode having a enddirected toward the object and so positioned with respect to the objectthat an ionic field is produced between the point and charged objectwhich reduces the potential of the object to the onset'potentia1 of thepointed electrode, and

means spaced from the pointed electrode in the direction of travel orthe object for producing an electric discharge of alternating polarityin such relationship to the object to neutralize the charge remaining onthe object regardless of the polarity of this charge.

6. Electric discharge equipment for neutralizing a charge oi.electricity on a travelling object, comprising a row 0! pointeddischarge electrodes spaced from each other and positioned to one sideof the path of travel of the object with the pointed ends directedtoward the object, the spacing between the pointed ends and object beingpredetermined to produce an electric discharge between the pointed endsof the electrodes and object and thereby reduce the charge on the objectto the "onset potential 01 the pointed electrodes, and means spaced fromthe row of discharge electrodes in the direction of the travel of theobject for producing an electric field of alternating polarity inproximity to the object to thereby neutralize the charge remaining onthe object.

'1. Electric discharge equipment for neutralizing a charge ofelectricity on a travelling object, comprising a discharge electrodehaving a pointed end directed toward the object and so positioned withrespect to the object that an ionic field is produced between the pointand charged object which reduces the potential of the object to theonset potential of the pointed electrode, a collecting electrode spacedfrom the discharge electrode in the direction of travel of the objectand having the same potential as the discharge electrode, an emittingelectrode spaced from the collecting electrode and connected to a sourceof alternating potential suflicient to produce an electric discharge ofalternating polarity between the emitting electrode and collectingelectrode. said emitting and collecting electrodes being so positionedwith respect to the object that the electrostatic field in the gapbetween the emitting and collecting electrodes neutralizes the chargeremaining on the object.

8. Electric discharge equipment for neutralizing a charge of electricityon a travelling object, comprising a row of pointed discharge electrodesspaced from each other and positioned to one side of the path of travelof the object with the pointed ends directed toward the object, thespacing between the pointed ends and object being predetermined toproduce an electric discharge hetween the pointed ends of the electrodesand object and thereby reduce the charge on the object to the "onset"potential of the pointed electrodes, 2. row of emitting electrodesspaced from the row of discharge electrodes in the direction of travelof the object and connected to a. source of alternating a collectingelectrode electrically connected to the row oi. discharge electrodes andoperatively positioned with respect to the emitting electrodes andobject to produce an electric discharge of alternating polarity betweenthe emitting electrodes and collecting electrode .suflicient toneutralize the charge remaining on the object.

GAMES SLAYTER.

